This is a competing continuation application for a Specialized Center of Research in Osteoporosis at Creighton University. It responds to an RFA issued by NIAMS, and is designed to continue the SCOR in Osteoporosis which was begun in September, 1987. The theme of the previous SCOR and of this renewal application is research into the Etiology, Prevention and Treatment of osteoporosis. The 10 projects in this proposal include 2 that are continued from the previous SCOR, and 8 that are new. They will join 7 other current projects. The projects in this application are; 1) Bone Histomorphometry Before and After Menopause, 2) Continuous Low-Dose Estrogen/Progestin in Elderly Women, 3) Factors Influencing Food Calcium Bioavailability, 4) Calcium Absorptive Physiology, 5) Bone Health and Non-Skeletal Illness, 6) Treatment of Calcium Deficiency, 7) Control of Bone Mass in the Aged, Osteopenic Skeleton, 8) In vivo Loading to Define Training Principles for Bone, 9) Mechanism of Fatigue Damage Due to Overuse in Bone, and 10) The Daily Experience of Osteoporosis: A Quantitative Study. Each of these studies relates to the theme of the SCOR. Etiology is a focus in projects 1,3,4,5,7, and 9. Prevention is a focus in projects 1-9. Treatment is a focus in projects 2,6,7,8 and 10. This group of projects continues our commitment to human research in osteoporosis, and builds on our growing thrust in animal work. It also extends our more recent entry of five years ago into the area of the regulation of bone cell function by mechanical forces. These projects will advance the understanding of osteoporosis, and will bring us closer to reducing the morbidity and mortality associated with this condition which afflicts nearly half of our elderly female population.